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View Full Version : What theory does the graviton come from?



Atraxani
2006-Mar-20, 04:10 AM
Where did the term originate? Who came up with it? What's the earliest use of the term?

I am unable to find this out. Thanks.

Argos
2006-Mar-21, 02:20 PM
The Graviton relates to Quantum Gravity theories (strings, superstrings, M-theories...). The 'on' suffix is generally applied to particles. The Graviton would be a particle of gravity. No clue about whos coined the term.

Atraxani
2006-Mar-21, 02:47 PM
The wikipedia article on general relativity (http://en.wikipedia.org/wiki/General_relativity) stetes that:


Gravitons (http://en.wikipedia.org/wiki/Gravitons): According to quantum mechanics (http://en.wikipedia.org/wiki/Quantum_mechanics), gravitational radiation must be composed of quanta called gravitons. General relativity predicts that these will be spin-2 particles (http://en.wikipedia.org/wiki/Subatomic_particle). They have not been observed.

Is that correct? I was under the impression that general relativity couldn't make any predictions concerning particle spin.

This article says that:



There should be a messenger particle, the graviton, and from its classical description in general relativity we can surmise it has spin 2.

http://tena4.vub.ac.be/beyondstringtheory/generalrelativity.html

Is the article incorrect?

Thanks in advance

Tensor
2006-Mar-21, 07:58 PM
The wikipedia article on

snip...

Thanks in advance

Particle spin can, in some cases, be predicted based on the type of properties the particular radiation has. We suspect gravity moves at c, which means it has to be massless. We've only seen attraction with gravity, so it would have to have an even, integer spin (particles with even integer spin only attract, odd integer spin can attract or repel). The other part of spin has to deal with polarization. As for what number, the spin would be, Photons have 1 polarization state, and so are spin 1. Gravitational radiation should have 2 polarization states, and thus should be spin 2. Note it has an even, integer spin, which matches the attraction requirement. Which is why you see the graviton spoken of as being a massless, spin 2 particle.


(Note for experts in QM, I know quantumly, spin and polarization are not quite identical, but can be kinda sorta thought of as related, and I'm trying to keep this simple).

Duane
2006-Mar-22, 12:50 AM
How would this particle relate to the Higgs boson?

Tensor
2006-Mar-22, 04:17 AM
How would this particle relate to the Higgs boson?

heheheheh, if I knew that, I could probably book my trip to Sweden. I'd tell you my thoughts, but this isn't the ATM forum.

Atraxani
2006-Mar-22, 05:15 AM
Particle spin can, in some cases, be predicted based on the type of properties the particular radiation has. We suspect gravity moves at c, which means it has to be massless. We've only seen attraction with gravity, so it would have to have an even, integer spin (particles with even integer spin only attract, odd integer spin can attract or repel). The other part of spin has to deal with polarization. As for what number, the spin would be, Photons have 1 polarization state, and so are spin 1. Gravitational radiation should have 2 polarization states, and thus should be spin 2. Note it has an even, integer spin, which matches the attraction requirement. Which is why you see the graviton spoken of as being a massless, spin 2 particle.

Thanks for the excellent response.

Nereid
2006-Mar-22, 08:24 AM
Contrary to what's on the wiki page (or maybe extending it), 'the graviton' cannot be simply the gravitational force carrier counterpart to the photon.

'the graviton', as a particle in QM (a theory), may have the properties outlined by Tensor. However, any such particle must also be 'present' in GR.

However, GR and QM are mutually incompatible, at many levels (fortunately for us - or otherwise! - this incompatibility is manifest in physical regimes that are far, far beyond our current abilities to 'see'). Whatever theory, or theories, emerge that successfully incorporate both GR and QM (as 'limit cases') may include something like a graviton. It (they) may also be radically different, and not include anything at all like 'the graviton'.